In earlier studies we have used specially designed microspheres bound to concanavalin A (Con A) to map the distribution of glycoproteins on the surface of photoreceptor rod cells by scanning electron microscopy (SEM). Electrophoretic analysis of rod outer segment (ROS) membrane proteins indicate that rhodopsin and a 270,000 mol. wt. glycoprotein serve as Con A receptors. We now propose to extend these studies to 1) determine the distribution, orientation and dynamic properties of rhodopsin and other minor glycoproteins in ROS disk and plasma membranes and inner segment plasma membranes of vertebrate rods; 2) to isolate and characterize the minor glycoproteins; 3) to localize Na K ion ATPase along intact rod cells; and 4) to isolate pure populations of disk and plasma membrane vesicles. Lectins and antibodies chemically coupled to iron-containing fluorescent microspheres will be used to label specific glycoproteins. The microspheres will serve as visual markers for mapping the distribution and orientation of specific glycoproteins on photoreceptor membranes by fluorescent, scanning and transmission electron microscopy. Such reagents will also be used to isolate membrane vesicles with a defined orientation by affinity density and magnetic separation techniques. Cell surface labeling studies will be correlated with biochemical studies of membrane glycoproteins employing electrophoresis, affinity chromatography and limited proteolysis. Ouabain-microsphere conjugates will be used to localize Na K ion ATPase along photoreceptor cells by SEM. These highly sensitive and specific labeling techniques will be used to gain further insight into the molecular organization of photoreceptor membranes and the molecular basis of visual excitation.